Carbon-trap alloys for liquid sodium

ABSTRACT

Special binary alloys (Fe-Ti, Fe-V, Fe-Mn) possess the optimum kinetic and thermodynamic properties which make them efficient carbon traps for full-flow liquid sodium cooled system, and thus can be effectively utilized to protect heat exchangers from damage due to carburization during sodium circulation. These alloys do not require heating above normal operating temperatures, for efficient carbon trapping.

United States atent [1 1 Armijo Dec. 10, 1974 CARBON-TRAP ALLOYS FORLIQUID SODIUM [76] Inventor: Joseph S. Armijo, 19310 Portos Ct.,

Saratoga, Calif. 95070 [22] Filed: Nov. 2, 1973 [21] Appl. No.: 412,395

[52] US. Cl. 176/38, 75/123 M, 75/123 N, 75/123 J [51] Int. Cl G2lc15/02 [58] Field of Search 75/123 M, 123 N, 123 J; 176/37, 38

[56] References Cited OTHER PUBLICATIONS Hansen, Constitution of BinaryAlloys,pp. 223-227, 1958.

Comstock, Titanium in Iron and Steel," pp. 163-165, 1955.

Primary Examiner-L. Dewayne Rutledge Assistant Examiner-Arthur J.Steiner Attorney, Agent, or FirmJohn A. Horan; Frederick A. Robertson;L. E. Carnahan 5 7 ABSTRACT 4 Claims, N0 Drawings CARBON-TRAP ALLOYS FORLIQUID SODIUM BACKGROUND OF THE INVENTION embrittle the IHX material anddegrade its thermal conductivity.

One prior known method for routine or emergency control of carbon iswith a bypass carbon trap, wherein the sodium coolant is at leastpartially circulated through a carbon trapping mechanism. The problemwith carbon trapping is that any efficient device must be as active ormore active a carbide former as stainless steel, and must remove thecarbon from the coolant far more rapidly than the stainless steel of theIHX or other component.

Previous attempts to make carbon traps have not been efficient becausean inadequate material was used as the carbon trap. For example, Type304 austenitic stainless steel has been used as a carbon trap materialin sodium cooled systems. However, this material will not operateefficiently as a carbon trap unless it is heated to temperaturessubstantially higher than the bulk sodium. The same problems areassociated with pure titanium (Ti), zirconium (Zr), or niobium (Nb)metals which have also been previously used as carbon traps.

Previous carbon trap metals and alloys have failed for kinetic reasons,i.e., the carbon must diffuse slowly through an austenitic or a carbidecrystal structure. This slow diffusion limits the rate of carbon pickupfrom the stream of liquid sodium coolant. Thus, with increased use ofliquid metal sodium as a coolant, a need exists for a simple yeteffective method of controlling carbon transport from one component toanother via the coolant.

SUMMARY OF THE INVENTION The invention described herein consists of aseries of alloys in which carbon diffusion is significantly faster thanin austenitic stainless steels, and which contain active carbideformers. These novel alloy binary alloys consist ofiron (Fe) andselected amounts of either titanium (Ti), vanadium (V), or manganese(Mn). These alloys are solid solutions in which the carbide formingelements (Ti, V, Mn) are uniformly distributed on an atomic scale.

Therefore, it is an object of this invention to provide carbon trapalloys for liquid metal coolant.

A further object of the invention is to provide alloys in which carbondiffusion is faster than in austenitic stainless steels, and whichcontain active carbide formers for trapping carbon being transported inliquid sodium.

Another object of the invention is to provide special alloys which serveto trap carbon contained in liquid sodium coolant and are solidsolutions in which the carbide forming elements are uniformlydistributed on an atomic scale.

Other objects of the invention will become apparent to those skilled inthe art from the following description.

DESCRIPTION OF THE INVENTION The invention comprises special alloys inwhich carbon diffusion is about 10 times faster than in austeniticstainless steels, and which contain active carbide formers. Such alloysare particularly useful in liquid metal cooled reactors to protectcomponents, such as heat exchangers, from damage due to carburizationduring sodium circulation. These novel alloys possess the optimumkinetic and thermodynamic properties which can make them efficientcarbon traps for full-flow sodium service in a nuclear reactor, becausethey do not require heating above normal operating temperatures forefficient carbon trapping.

As pointed out above, liquid sodium coolant in nuclear reactors, such asthe LMFBR, will transport carbon from the austenitic stainless steelcore and the ferritic steel steam generator to austenitic stainlesssteel components, such as the intermediate heat exchanger (IHX), causingembrittlement thereof and degrading of its thermal conductivity. Thepresent invention provides carbon trapping alloys which are more activeas a carbide former than stainless steel, and thus remove the carbonfrom the sodium coolant far more rapidly than the stainless steel,thereby effectively protecting reactor components, such as the IHX, fromdamage due to carburization during sodium service.

Thespecial binary alloys constituting the invention comprise thefollowing for compositions; v

1. Iron (Fe) plus 0.5 to 30 wt.% titanium (Ti) 2. Iron (Fe) plus 0.5 to25 wt.% vanadium (V) 3. Iron (Fe) plus 0.5 to 5 wt.% manganese (Mn) Eachof the above alloys are solid solutions in which the carbide formingelements (Ti, V, and Mn) are uniformly distributed on an atomic scale.The crystal structure of each of these alloys (b.cc) is such, that theirrate of carbon pickup will be about l0 times faster than the rate ofcarbon pickup by an austenitic (f.c.c.) stainless steel such as Type304. Further, since the activity of carbon is defined by the carbideforming elements, these alloys are as active carbide formers asstainless steels. Finally, since these are binary alloys the trapping ofcarbon will produce a two-phase moving boundary layer in which carbideparticles will be uniformly distributed in a b.cc matrix. Therefore, acarbon trap, utilizing these alloys will not plug up by forming acontinuous carbide layer.

Experiments conducted to varify the inventive concept show, for example,that the Fe-9 Ti alloy is approximately ten (10) times more effective intrapping carbon than stainless steel, and that Fe-Cr alloys areineffective. These test results are set forth in greater detailing inU.S.A.E.C. Report GEAP-l39l9-3 generated under the above-identifiedcontract with the Atomic Energy Commission.

Ithas thus been shown that with the binary alloys of this invention,efficient carbon traps for primary or secondary liquid sodium systemscan be provided, thereby overcoming the problems of the prior knowncarbon traps, and thus substantially advancing the state of the artrelating to carbon trapping.

While particular binary alloys have been described,

modifications might be accomplished by those skilled in the art, and itis intended to cover in the appended claims all such modifications ascome within the spirit and scope of the invention.

What I claim is:

1. In a sodium cooled nuclear reactor containing austenitic stainlesssteel components subject to damage due to carburization during sodiumcirculation, a material for trapping carbon and thereby preventingdamage to components due to carburization comprising a binary alloy inwhich carbon diffusion is faster than in austenitic steels and whichcontains an active carbide former, said binary alloy consistingessentially of Fe and a second element selected from the groupconsisting of 0.5 to 30 wt.'% Ti, 0.5 to 25 wt.% V, and 0.5 to 5 wt.%Mn.

2. The material for trapping carbon defined in claim I, wherein saidalloy is consisting essentially of Fe 0.5 to 30 wt.% Ti.

3. The material for trapping carbon defined in claim 1, wherein saidalloy is consisting essentially of Fe 0.5 to 25 wt.% V.

4. The material for trapping carbon defined in claim 1, wherein saidalloy is consisting essentially of Fe 0.5 to 5 wt.% Mn.

1. IN A SODIUM NUCLEAR REACTOR CONTAINING AUSTENITIC STAINLESS STEELCOMPONENTS SUBJECT TO DAMAGE DUE TO CARBURIZATION DURING SODIUMCIRCULATION, A METAL FOR TRAPPING CRBON AND THEREBY PREVENTING DAMAGE TOCOMPONENTS DUE TO CARBURIZATION COMPRISING A BINARY ALLOY IN WHICHCARBON DIFFUSION IS FASTER THAN IN AUSTENITIC STEELS AND WHICH CONTAINSAN ACTIVE CARBIDE FORMER, SAID BINARY ALLOY CONSISTING ESSENTIALLY OF FEAND A SECOND ELEMENT SELECTED FROM THE GROUP CONSISTING OF 0.5 TO 30WT,% V, AND 0.5 TO 5 WT.% MN. AND RECEIVING THEREIN SAID FUEL ELEMENTSTO MAINTAIN THEM IN A VERTICALLY EXTENDING POSITION BETWEEN ENDFITTINGS; MEANS ASSOICATED WITH SAID UPPER CORE ALIGNMENT STRUCTURE ANDSAID UPPER END FITTINGS FOR LATERALLY RESTRAINING EACH OF SAID FUELASSEMBLIES WHILE ALLOWING LIMITED AXIAL MOVEMENT THEREOF: A PLURALIGY OFALIIGNMENT POSTS AFFIXED TO EACH OF SAID LOWER END FITTINGS ANDEXTENDING DOWNWARDLY THEREFROM; A POST ENGAGING MEANS, ASSOCIATED WITHEACH OF SAID ALIGNMENT POSTS, AFFIXED TO AND EXTENDING UPWARDLY FROMSAID LOWER CORE SUPPORT STRUCTURE FOR SLIDABLE RECEIVING AND LATERALLYRESTRAINING SAID ALIGNMENT POSTS, SAID POST ENGAGING MEANS INCLUDING ASPRING CONTAINMENT SECTION HAVING SPRING RETAINING MEANS AT ITS LOWEREND AND MEANS FOR TRANSMITTING DOWNWARD FORCE ON SAID SPRING RETAININGMEANS TO SAID LOWER CORE SUPPORT STRUCTURE; AND COIL SPRING MEANS INPARTIAL COMPRESSION DISPOSED WITHIN SAID SPRING RECEIVING SECTION,REACTING DOWNWARDLY AGAINST SAID LOWER CORE SUPPORT STRUCTURE ANDREACTING UPWARDLY THROUGH SAID LOWER END FITTINGS TO URGE SAID FUELASSEMBLIES IN ENGAGEMENT WITH SAID UPPER CORE ALIGNMENT STRUCTURE. 2.The material for trapping carbon defined in claim 1, wherein said alloyis consisting essentially of Fe + 0.5 to 30 wt.% Ti.
 3. The material fortrapping carbon defined in claim 1, wherein said alloy is consistingessentially of Fe + 0.5 to 25 wt.% V.
 4. The material for trappingcarbon defined in claim 1, wherein said alloy is consisting essentiallyof Fe + 0.5 to 5 wt.% Mn.